Known techniques of transmitting inbound messages in a multichannel communication system which includes a plurality of selective call devices and which has a plurality of inbound channels are techniques which use a scheduled inbound transmission protocol and techniques which use a contention (unscheduled) inbound transmission protocol. An example of a scheduled transmission protocol is a transmission protocol in which at least one predetermined time slot is reserved on at least one predetermined inbound channel for each selective call device which is active in the communication system. Another example of a scheduled inbound transmission protocol is a transmission protocol in which a selective call device is notified of a demand response time slot to be used for transmitting a long inbound message. The notification is given within an outbound message which is sent in response to a short inbound message sent by the selective call device informing the communication system of the existence of the long inbound message.
An example of a contention inbound transmission protocol is an ALOHA protocol, which is well known to one of ordinary skill in the art. Inbound messages sent by an ALOHA protocol are typically transmitted as soon as they are generated. When two such messages happen to be transmitted on one channel such that some portions are transmitted simultaneously, one or both messages may not be received correctly. In this event, the messages are not acknowledged by the communication system and each selective call device repeats the message after a random delay.
The communication system may be a wireline or optical or radio communication system. In a wireline system, the inbound channels may be separated by physically different wires, or may separated (particularly in the case of high speed wireline systems) by band limited channels, or by both. In optical or radio communication systems, the channels are typically separated by band limited channels, but may be alternatively or additionally be separated by time division duplexing.
Some systems which have an outbound signaling protocol which is synchronous are designed so that the selective call devices acquire synchronism to the outbound signaling protocol and use a scheduled inbound transmission protocol, because a scheduled inbound transmission protocol is typically more efficient than a contention inbound transmission protocol for several types of inbound messages, such as some demand responses and acknowledgments. However, a contention transmission protocol can be typically more efficient for other types of inbound messages, such as some unsolicited inbound messages. Thus it can be desirable to provide for both types of inbound transmission protocols.
Prior art systems typically provide for a mix of scheduled and contention inbound transmission protocols by designating some types of messages to be transmitted using an ALOHA protocol and other types of messages to be transmitted using a scheduled transmission protocol. A selective call device then uses the indicated technique on an authorized inbound channel. The authorized inbound channel is typically any one of the inbound channels which the selective call device is designed to use.
However, in some communication systems, some inbound channels are not as efficient when used for inbound messages when using an ALOHA protocol. For example, in some radio communication systems, some inbound radio channels (hereafter, "restricted channels") are geographically restricted to areas smaller than an area covered by the outbound radio channels while other inbound radio channels have coverage substantially equivalent to the outbound radio channels. The restricted channels are not as efficient for transmitting inbound messages using an ALOHA protocol, because the selective call device may not be in the coverage area of the restricted channel.
Thus, what is needed is an improved technique of selecting an inbound channel which is to be used for transmitting an inbound message using an ALOHA protocol in a communication system.